1. Field of the Invention
Catalyst layers on ceramic substrates for the conversion of exhaust gases from internal-combustion engines.
The invention relates to space-saving means for the afterburning and detoxification of the exhaust gases from road vehicle internal-combustion engines, specifically with regard to the devices for supercharging them.
In particular, it relates to a method of applying a catalyst layer consisting of precious metals and/or precious metal compounds to a substrate of ceramic material.
2. Discussion of Background
Catalytic converters for converting the exhaust gases from internal-combustion engines (spark-ignition and diesel engines) are being used increasingly, in particular in view of environmental pollution, above all for road vehicles. The relevant legal regulations are becoming continually more stringent and it is therefore in the interests of the public at large to utilise all the possibilities of exhaust emission control. The application of electrically conducting tin oxide layers is known from the literature. A common method is spraying with subsequent pyrolysis.
The following publications are cited as prior art:
Edgar Koberstein, Katalysatoren zur Reinigung von Autoabgasen (Catalystic Converters For Automobile Exhaust Emission Control), Chemie in unserer Zeit, 18th year, 1984, No. 2, pages 37-45 PA0 Polat Oeser and Walter Brandstetter, Grundlagen zur Abgasreinigung von Ottomotoren mit der Katalysatortechnik, (Principles of Exhaust Emission Control from Spark-Ignition Engines using Catalyst technology), MTZ Motortechnische Zeitschrift 45 (1984) 5, pages 201-206 PA0 M. G. Nicholas, D. A. Mortimer, Ceramic/metal joining for structural applications, (1985 The Institute of Metals), Materials Science and Technology, September 1985, Vol. 1, pages 657-665 PA0 EP-A-O 143 956 PA0 Chopra, K. L., Mayor, S., and Pandya, D. K., Transparent Conductors a Status Review, Thin Solid Films 102 (1983), p.15 PA0 E. Shanthi, V. Dutta, A. Banerjee, and K. L. Chopra, Electrical and optical properties of undoped and antimony-doped tin oxide films, J. Appl. Phys. 51(12), December 1980 PA0 I. S. Mulla, H. S. Soni, V. J. Rao, A. P. B. Sinha, Deposition of improved optically selective conductive tin oxide films by spray pyrolysis, Journ. of Materials Science 21 (1986), 1280-1288.
In EP-A-O 143 956, a volumetric supercharger (pressure-wave machine) for a road vehicle engine is described, the rotor of which is at the same time designed as a catalyst substrate. This can dispense with the need, at least to some extent, of a separate means of detoxifying the exhaust gases. However, problems arose in the coating of a rotor consisting of a ceramic material, since the rotor, and consequently the catalyst layer, are exposed to very high mechanical and thermal stresses (circumferential forces, temperature changes). The layers must be firmly anchored and must not peel off during operation.
Therefore, there is a great need for further development and perfection of the catalyst coating technique.